In general, there is a magnetic tape apparatus having a magnetic tape as a recording medium as one of external storage apparatuses for a computer. As a prevailing magnetic tape apparatus, a magnetic tape cartridge employing a tape having a width of 0.5 inch and being loaded with the tape pulled out automatically from a reel in a case is used extensively. The magnetic tape cartridges by a required number are loaded (entry) in a magnetic tape library apparatus (hereinafter, referred to as a library apparatus) and are loaded selectively in a magnetic recording and reproducing device for writing and reading data.
The library apparatus includes a medium storing shelf having a plurality of cells for storing magnetic tape cartridges, the magnetic recording and reproducing device configured to perform a data recording and reproducing process, and a transporting device configured to transport the magnetic tape cartridges between the medium storing shelf and the magnetic recording and reproducing device.
In the case of a large sized library apparatus, since the medium storing shelf having a number of cells arranged in row and a plurality of magnetic recording and reproducing devices are connected to each other and assembled into a casing (housing), a large margin of an error which occurs at the time of assembly (hereinafter, referred to as an assembly error) is resulted. When the assembly error is large as described above, accurate positioning of the transporting device with respect to the respective cells in the medium storing shelf is difficult only with values estimated in a designing stage.
Accordingly, as means for correcting the positional displacement as described above, the library apparatus is provided with a position detecting device which detects a relative position between the medium storing shelf and the transporting device, and detects a relative position between the magnetic recording and reproducing devices and the transporting device. The position detecting device includes a flag provided on a front surface portion of the cells and the magnetic recording and reproducing devices, and an image pickup device provided on the transporting device and configured to pick up an image of the flag. Then, the position detecting device obtains an amount of positional displacement on the basis of image data of the flag the image of which is picked up by the image pick up device, and reflects the amount of displacement at the time of transporting process as a correcting amount, so that accurate positioning is achieved.
In the related art, as illustrated in FIG. 1A and B, a flag 1 for performing the position detection is fixed to a cell 3 using a holder 2 or the like. Also, in order to achieve the accurate positioning, at least three positions are required as positions to dispose the flag, so that the flags 1 are fixed to a plurality of cells 3 of the medium storing shelf in general (refer to Japanese Laid-open Patent Publication No. 2007-139617).
As known publicly, increase in number of magnetic tape cartridges to be stored in the library apparatus and downsizing thereof are desired. However, in the method of fixing the flags on the cells as in the related art, the magnetic tape cartridges cannot be mounted on the cells having the flag thereon. In other words, assuming that the number of the cells provided in the medium storing shelf is N, the number M of storage of the magnetic tape cartridges which can be stored actually in the medium storing shelf is M=N−3.
Therefore, the method of disposing the flags in the related art has a problem that the efficiency of storage of the magnetic tape cartridges in the medium storing shelf is lowered (in the example illustrated above, the efficiency is lowered by three cartridges). Also, when an attempt is made to store the N pieces of magnetic tape cartridges, it is necessary to provide three cells separately in the medium storing shelf and, in this case, there arises a problem of upsizing of the library apparatus.